Nodatime Test Conventions

Noda Time Test Conventions

Conventions observed in the existing test suite. Match these rather than introducing a new style — consistency across ~150 test files matters more than any one file being "improved."

Framework

• NUnit 4, but assertions go through classic aliases set up in GlobalUsings.cs:

  global using Assert = NUnit.Framework.Legacy.ClassicAssert;
  global using CollectionAssert = NUnit.Framework.Legacy.CollectionAssert;
  global using StringAssert = NUnit.Framework.Legacy.StringAssert;
  

• Dominant assertion style: Assert.AreEqual(expected, actual), Assert.IsTrue/IsFalse, Assert.Throws<T>(...). Constraint-based Assert.That(x, Is.EqualTo(y)) shows up occasionally (mostly comparison tests) — fine to use but not the default.
• Assert.Multiple(() => { ... }) to group related assertions in one test.

File & class organization

• Test class name = [TypeName]Test (e.g. LocalDateTest).
• Split into partial classes by concern, not by size: LocalDateTest.Construction.cs, LocalDateTest.Comparison.cs, LocalDateTest.Operators.cs, LocalDateTest.Conversion.cs, etc. Each partial file is declared DependentUpon the main file in the .csproj. When adding a new concern area, add a new partial file rather than growing an existing one indefinitely.

Test method naming

MethodName_Scenario_ExpectedResult, e.g.:

• FromDays_Int32, FromHours_Double
• Construction_NullCalendar_Throws
• ComparisonOperators_DifferentCalendars_Throws
• IComparableCompareTo_WrongType_ArgumentException

Plain descriptive names (DefaultConstructor, Equality, Comparison) are also fine for single-scenario tests.

TestHelper.cs — use it, don't reinvent it

src/NodaTime.Test/TestHelper.cs is the shared toolbox. Check it before writing manual equality/comparison/exception assertions:

• Equality contract: TestHelper.TestEqualsStruct(value, equalValue, ...unequalValues), TestEqualsClass, TestObjectEquals — exercise reflexivity, symmetry, hash-code consistency, and IEquatable<T> in one call.
• Comparison contract: TestCompareToStruct, TestCompareToClass, TestNonGenericCompareTo.
• Operator contract (reflection-driven): TestOperatorEquality, TestOperatorComparison, TestOperatorComparisonEquality.
• Exception-shape helpers: AssertInvalid, AssertArgumentNull, AssertOutOfRange, AssertOverflow, AssertValid.
• XML round-trip: AssertXmlRoundtrip(value, expectedXml), AssertParsableXml, AssertXmlInvalid<T>(xml, expectedExceptionType).

Typical pairing for a new value type:

[Test]
public void Equality()
{
    var equal = new Instant(1, 100L);
    var different = new Instant(1, 200L);
    TestHelper.TestEqualsStruct(equal, equal, different);
    TestHelper.TestOperatorEquality(equal, equal, different);
}

Data-driven tests

• [TestCase(...)]: default choice for a handful of inline values.
• [TestCaseSource(nameof(...))]: for larger or generated datasets — source a static readonly array, or a property returning TestCaseData[] when each case needs .SetName(...) for readable output.
• Pattern-parsing tests (src/NodaTime.Test/Text/) extend PatternTestBase, supplying static Data[] fields (InvalidPatternData, ParseOnlyData, FormatOnlyData, FormatAndParseData) that the base class wires into [TestCaseSource] automatically.

Culture-dependent tests

• Use CultureSaver (src/NodaTime.Test/CultureSaver.cs) to scope a culture change and auto-restore it:

  using (CultureSaver.SetCultures(Cultures.FrFr))
  {
      // assertions under fr-FR
  }
  

• Pull named test cultures from Text/Cultures.cs (Cultures.Invariant, Cultures.FrFr, Cultures.AllCultures, …) rather than constructing CultureInfo ad hoc — several are deliberately tweaked (e.g. lowercase month names) to catch culture-handling bugs.

Categorization & skipping

• [Category("Slow")] + [Explicit] for expensive tests (e.g. BCL cross-checks over a full calendar history) that shouldn't run by default.
• [Category("Overflow")] for overflow-boundary cases.
• Ignore.When(condition, "reason") (src/NodaTime.Test/Ignore.cs) for runtime-conditional skips (e.g. platform not supported), instead of Assert.Ignore directly.
• #if NET7_0_OR_GREATER / similar for TFM-specific tests, matching the multi-targeting already in the .csproj.

What NOT to do

• Don't hand-roll equality/comparison/operator tests when a TestHelper contract tester covers it.
• Don't introduce a new assertion library or constraint style wholesale — this project standardized on classic Assert.*.
• Don't flatten a partial-by-concern test class back into one file, and don't split a single concern across multiple files.